I obtained a card in a trade. It is a Chris Johnson Contenders rookie auto. It is slabbed by BGS and the auto is graded a 10. But instead of a card grade, it says 'Authentic'. I never thought anything of it but has been told that it happens because the card is damaged. I looked over the card myself, the best I could and the card doesn't appear to have any noticeable damage.

So why do cards get labeled like this and how does that affect the value of the card?